1. Field of the Invention
The invention relates to a circuit configuration for on-screen image inseting or inset-image keying in a television set having only one tuner, including a control device for switching over the tuning frequency of the tuner in such a way that a first image or picture signal of a first program can be used for displaying a large image, and a second image or picture signal of a second program can be used for displaying a small image that can be keyed or set into the large image, a switchover device being connected downstream of the tuner and being controllable by the control device for supplying the first image or picture signal furnished by the tuner to a large-image signal route and alternately briefly supplying the second image or picture signal to a small-image signal route having a small-image memory device, and means for reading out and keying the small image stored in the small-image signal route into the large image on a picture tube of the television set.
2. Description of the Related Art
One such circuit configuration is known from German published, non-prosecuted application DE-OS 24 13 839, corresponding to published French application No. 2 265 235. In order to provide for inset-image keying, the familiar analog signal route (tuner, medium-frequency amplifier, video amplifier, horizontal and vertical deflection stage, and picture tube) for representing an image in a television set is expanded with a memory and switchover device, with which an image content to be reproduced for a small image to be keyed into the large image, can be stored and read out. The memory and switching device is controlled by the outputs of the medium frequency amplifier and by the horizontal deflection stage. In turn, the switch device switches over the tuner line by line between two tuning frequencies, in such a manner that during certain lines of the large image a different program, which is intended to be shown as a small image, is received. At the same time the video amplifier is connected to the memory device, as a result of which the lines of the other program being received are inscribed individually and in succession into the memory device, which is generally constructed as a CCD memory.
The memory device then outputs the information inscribed therein to the video amplifier whenever the electron beam scanning the screen arrives in the vicinity of the image cutout for the small image.
However, using that kind of circuit configuration for inset-image keying is at the very least problematic, particularly in terms of the line-by-line switchover of the tuner and the associated high switchover speed. Satisfactory picture quality for the person viewing the screen is unattainable with the known circuit configuration.
Other possibilities for inset-image keying in a television set have been proposed in German published, non-prosecuted application DE-OS 28 08 188 and U.S. Pat. No. 4,249,213, for instance. They provide two separate signal routes for receiving two television programs, each having at least one tuner with a medium frequency amplifier connected to the output side thereof. Although such a structure can be considered optimal in terms of the inset-image keying, nevertheless the high technical expense dictated by the two separate signal routes only allows it to be used for television sets in the upper price category.
It is accordingly an object of the invention to provide a circuit configuration for inset-image keying in a television set having only one tuner, which overcomes the hereinaforementioned disadvantages of the heretofore-known devices of this general type and with which the inset-image keying can be attained in a simple manner.